1. Field of the Invention
Methods and apparatuses consistent with the present invention relate to detecting an end of response signal of a Radio Frequency Identification (RF-ID) tag, and more particularly, to detecting an end of response signal of an RF-ID tag, with which a reader of an RF-ID system, which sends out a command signal to the RF-ID tag, can detect an end of signal (EOS) of a response and therefore send out a next command signal in a predetermined time.
2. Description of the Related Art
Within a distance of about 1 m, a related art RF-ID technology enables wireless receiving and reading of the stored information of an RF-ID tag though a reader thereof, without requiring any physical contact.
An RF-ID tag is usually attached to a product in the form of a chip and operates as a transponder. Thus, the RF-ID tag provides information about the product from its production to purchase.
A reader usually operates as a transceiver, which wirelessly transmits and receives signals with RF-ID tag through an antenna, and thus, receives and reads the information received from the RF-ID tag.
FIG. 1 shows a command signal sent from a related art reader and a response signal received from an RF-ID tag. The related art reader sends out a command signal 110 with a continuous wave CW to an RF-ID tag, and the RF-ID tag responds with a response signal 120, using a backscattering technique, when the condition suits the received command signal.
According to the related art standards, the backscattered response signal has a fixed length and is received from the RF-ID tag within a certain fixed time after the transmission of the command signal from the reader.
However, when a related art RF-ID system supporting EPCGlabal Class-1 Generation 2 sends out command signals, it receives backscattered response signals within different times according to respective lengths of the RF-ID tags. The reader has to send out command signal to the RF-ID tag within a certain fixed time.
Accordingly, a reader has to know the end of the response signal having a shortest time to calculate the start of transmission of the next command signal.
If the response signals received from the RF-IF tag have different bit length, the End Of Signal (EOS) of the received response signals cannot be known within a short time. Further, if the EOS of the response signals is not known within a predetermined fixed time, the RF-ID tag will turn to reset status, and the reader, which fails to find out the EOS of the response signal within the time limit, takes it as a reception failure and thus repeats communication with the RF-ID tag.